Carbon dioxide storage



Jan. 16, 1951 s, c, MARSH 2,538,023

CARBON DIOXIDE STORAGE Filed Sept. 26, 1944 3 Sheets-Sheet 3 l N V15 NTOR Patented Jan. 1951 CARBON DIOXIDE STORAGE Sidney Clarke Marsh,Hohoku s, N. 1., assignor to Specialties Development Corporation,Bloomfield, N. J., a corporation of New Jersey Application September 26,1944, Serial No. 555,876

9 Claims. 1

This invention relates to the storage of normal- 1y gaseous phasechangeable material, and particularly to a method and apparatus forliqueiying such material in solid phase, storing the liquefied materialand controlling the temperature thereof by a reversible cyclerefrigerating system.

In storing a normally gaseous phase changeable material, such as carbondioxide and the like in large quantities, in one container, it isdesirable to refrigerate the stored material to maintain it at a lowtemperature and at a corresponding low pressure, whereby the wallthickness of the container may be reduced, with consequent advantages,such as saving in weight, material and cost.

In accordance with this invention, it is proposed to charge a relativelylarge storage container with material such as solid carbon dioxide, andto liquefy the charge for storing the same in the container at a lowtemperature and its corresponding vapor pressure. It has been found thata reversible cycle refrigerating system or unit may be utilized for thispurpose, wherein, during operation in one direction, hot refrigerantserves to effect liquefaction of the solid carbon dioxide and, duringoperation in the opposite direction, cold refrigerant serves to maintainthe liquid carbon dioxide at its predetermined low temperature.

Accordingly, an object of the invention is to provide a method andapparatus for liquefying and/or storing normally gaseous phasechangeable material in a more effective way than heretofore practiced.

Another object is to more effectively liquefy and store a large quantityof such material in a single container.

Another object is to provide a system or apparatus wherein therefrigerant employed in the course of supplying heat to liquefy solidmaterial thereafter maintains the liquefied material at a predeterminedtemperature.

Another object is to provide a storage chamber or tank especiallyadapted to receive solid material without damage to the tank.

Another object is to provide a tank or storage chamber having heatexchange means therein adapted to more effectively operate both as anevaporator and a condenser in removing heat from and supplying heat tothe stored material.

A further object is to provide a system or apparatus of the aboveindicated character which is simple and durable in construction,economical to manufacture and eflective its operation.

invention in practice.

Other and further objects of the invention will be obvious upon anunderstanding of the illustrative embodiment about to be described, orwill be indicated in the appended claims, and various advantages notreferred to herein will occur to one skilled in the art upon employmentof the A preferred embodiment of the invention has been chosen forpurposes of illustration and description and is shown in theaccompanying drawings, forming a part of the specification, wherein:

Figure 1 is a diagrammatic view, illustrating an embodiment of a systemor apparatus, in accordance with the invention, for practicing themethod thereof.

Figure 2 is a sectional view of a novel storage tank employed in thesystem, parts being shown in full and others being broken away.

Figure 3 is a diagrammatic view of a modification of the invention asshown in Figure 1.

Figure 4 is a view similar to Figure 3 of the invention in furthermodified form.

The system in general Referring to Figure 1, a reversible cyclerefrigerating system, for practicing the method of the invention,comprises a conduit circuit including valves l to I5 inclusive, in whichcircuit are disposed, heat exchange means such as a 0011 I1 positionedin a storage chamber, structure or tank It, heat exchange units" and I9, an expansion valve 20, a liquid receiver 22, a dehydrator 23, anexpansion valve 24, heat exchange means 26 having a fanfl, a refrigerantcompressor 28, and pressure gauges 29 and 30.

The valves I to [5, inclusive, as shown, are of the hand operated typeand areadap ted to be manipulated to condition the circuit for itscycles of operation. If desired, the valves may be operatedautomatically by suitable control means such as a fluid pressure mediumor electrical circuit to effect reversal of the cycles of operation.

The expansion valves 20 and 24, of Figure l, are of the automatic, orfixed orifice, type.

The system in detail In the system, the coil I1 is connected from itslower end by a conduit 32 to the valve I,

to the expansion valve 24 and the valve 4, through a conduit 42 to thevalve 5, through a conduit 44 to the valve 6, and through a conduit 46and the heat exchange units I8 and I9, to the upper end of the coil I1.

The valve II is connected by a conduit 48, at one side, to the conduit46, and at the other side, by a conduit 58 to the valve I8. The valve I8is connected by a conduit 52 to the valve 9, which is connected by aconduit 54 to the conduit 36.

The valve 1 is connected by a conduit 56 to the conduit 32, and to theexpansion valve 28 by a conduit 58, the valve 28 being connected by aconduit 68, to the valve 8 which is connected by a conduit 62 to theconduit 38.

The compressor 28 is connected, at one side by a conduit 64, to theconduit 58, and atthe other side by a conduit 66 to the conduit 44. Thepressure gauges 29 and 38 are connected in the con duits 64 and 66 atopposite sides of the compressor, respectively.

The heat exchange means 26 is connected by conduits 68 and 18 betweenthe conduits 42 and The heat exchange unit I8 is connected, at one side,by a conduit 16, to the valve I2 which is connected by a conduit 18 tothe conduit 32, and, at the other side. by a conduit 88, to the valveI3, which is connected by a conduit 82 to the conduit 34. The heatexchange unit I9 is connected at one side by a conduit 86 to the valveI5, which is connected by the conduit 88 through the valve I3 and theconduit 82 to the conduit 34. The other side of the unit I9 is connectedby a conduit 88 to the valve I4 which is connected by a conduit 98 tothe conduit 34.

The above described conduits are for illustrative purposes only, itbeing obvious that they may be otherwise arranged to accomplish the samefunction.

The tank Referring to Figure 2, the tank I6 comprises a base structure92 including legs 94, feet 96 and cross brace means 98, the legs beingfitted at the upper ends, as by curved portions I88, to a bottom elementI82 of an upright outer shell I83 having a cylindrical side wall I84,into the top of which depends a cup-shaped closure element I86, theparts of the tank, as thus far described, preferably being formed ofmetal and secured together as by welding.

An inner shell H8 is disposed Within the outer shell, and constitutesthe storage chamber for the material. The shell II8 comprises a topmember H2, cylindrical side wall section I I4, and a bottom member II6,the top member Hz and the bottom member II6 being welded to the sidewall section H4 at H8 and I28, respectively.

The inner shell I I8 is of sufilciently smaller diameter than the outershell I83 to provide an eiiective insulating space I22, shown, in thisinstance, as a vacuum space for certain applications, or which maycontain suitable insulating medium or the like.

The top member I I2 of the inner shell I I8, and the top closure elementI86 of the outer shell I83, have adjacent registering apertures ofsubstantially oval or elliptical shape, on the minor axis of which thesection of Figure 2 is taken. An oval sleeve I24 is positioned in theseapertures and is welded to the member I I2 and the element I86 in sealedrelation thereto. The sleeve I24 provides an oval opening through whichsolid material may be placed into the inner shell, and

forms a downwardly facing shoulder I26 for a cover I28 conforming to thecontours of the oval parts set forth, and havin a seat I38 for a sealinggasket I32 adapted to engage the shoulder I26.

The cover I28, in cross section, is bowed upwardly to conform to thearch at the top of the inner shell H8, and has an internally screwthreaded aperture portion I34 for the reception of a relief valve I36.

A clamp member I38, of which there may be one or more, spans a portionof the oval aperture of the sleeve I 24. The member I38 engages thesleeve I24 and is connected to the cover I28, as

by a bolt or bolts I48, each having a nut I42 thereon for clamping thecover I28 in closed position.

A metal ring I46, of angle section, is secured as by welding, inposition in the top closure element I86 to form a seat I48 for a sealinggasket lI58 on which is disposed a top insulating cover The cover I52 isof hollow wall character, containing an insulating filler I54, andcomprises upwardly arched top and bottom wall elements I56 and I58,respectively, both of thin sheet metal, and the top element I56, whichis of simple inverted substantially cup-shape, is welded at its bottomedge, to the top side of the bottom element I58. The bottom element I58has an outer peripheral flat horizontal margin I68 forming a shoulderfor cooperation with the gasket I58. The cover I52 rests by gravity inclosed position, as illustrated, and is provided with handle means I59,as indicated in Figure 1.

At the bottom of the shell 8, a metal hood I62, made up of a disc topportion I64, and 9. cylindrical side wall portion I65 welded to theportion I64 and having openings I66, is provided for the top end of adischarge pipe I 68 extending through the bottom member H6 and thebottom element I82 and welded thereto. A brace I18 is provided betweenthe discharge pipe I68 and the bottom member H6, and a similar brace I12between the discharge pipe and the bottom element I82, and a cap,closure valve or other element I14 is provided at the lower end of thedischarge pipe I68.

The coil means The coil I1, as shown in Figure 2, comprises an uppernipple I 16 bridging the insulating space I22 and extends throughapertures in the inner cylindrical section H4 and the side wall I84 ofthe outer shell, in which apertures it is welded and sealed. The outerend of the nipple I16 is internally screw threaded for attachment to theconduit 46, and the inner end of the nipple I16 is adapted for thereception of a substantially single turn coil section I18 of metaltubing having its coil diameter nearly equal to the internal diameter ofthe inner cylindrical section H4. The lower end I19 of the coil sectionI18 is attached, as by coupling means I 80, to an upright pipe sectionI82, of substantial length, but only fragments of the top and bottom endsections of which are shown.

' The lower end of the upright pipe section I82 is similarly connected,as by coupling means I84, to the upper end I86 of a lower coil sectionI88 having, in this instance, about twelve turns. The lower end I98 ofthe coil section I88 is connected to a nipple I92, similar to the nippleI16 in its relation to the inner cylindrical section N4, the insulatingspace I22 and the outer side wall cylinder I84, and also having an outerend, similar to the outer end of the nipple I16, for attachment to theconduit 32.

A metal sleeve-like shield I84, having a diameter smaller than thediameter of the coil section I88, is disposed inside the coil section toprotect the latter from damage by impact with, or the weight of, thecharge of solid carbon dioxide to be disposed therein.

The upper single turn coil section I18 and the lower multiple turn coilsection I88 are thus arranged in accordance with the condition of therefrigerant, as it comes in warm condition from the high side of thecompressor 28.

The coil'section I18 at the upper portion of the tank provides for someheat transfer at or near the liquid level in the tank, while the coilsection I88 at the lower portion of the tank provides for the bulk ofthe heat transfer to take place at the lower portion of the tank wherethe solid carbon dioxide is disposed during the latter period of theheating cycle and-where the liquid is located during storage. Thisarrangement gives the best-heat transfer to meet allconditiom of use ofthe apparatus and is particularly advantageous during the heating cycle.

Operation HEATING CYCLE For the heating cycle, valves I, 2, 3, 4, 6 andI8 will be open, and the valves 5,1, 8, 8, II, I2, I3, I4, and I will beclosed.

In operation, to convert the solid material in the tank I6 to liquidstate, and starting at the high pressure side of the compressor 28, withvalve 5 closed and valve 6 open, compressed hot refrigerant vapor passesfrom the compressor 28, through the conduits 66 and 44, the valve 6 andthe conduit 46 to the nipple I16.

From the latter, the hot refrigerant passes through the single turn coilsection I18, the upright pipe section I82 and the lower coil sectionI88, where heat is given up, as aforesaid, and the refrigerant icondensed to a liquid by the low temperature of the solid material(about -118 F. when storing carbon dioxide). This heat exchange means inthe foregoing instance acts as a condenser.

With the valves 1, 8, 8, I2, I3, I4 and I5 closed, and valves I, 2, 3and 4 open, the cold liquid refrigerant travels through the lower nippleI82, the conduit 32, the valve I, the conduit 34, the valve 2, and theconduit 36, to the liquid receiver 22. From the liquid receiver 22, theliquid refrigerant passes through the conduit 31 to the dehydrator 23,and, with the valve 8 closed and the valve 3 open, the liquid isexpanded through the expansion valve 24 into the heat exchange means 26which acts as an evaporator in the material heating cycle.

The expanded refrigerant is heated in the heat exchange means 26 by airblown thereon by the fan 21 and, with valves 8 and II closed, and thevalve I8 open, the refrigerant passes to the low pressure side of thecompressor 28 to complete the heating cycle.

During the heating cycle, by opening the valves I2, I4 and I5, andclosing-the valves I and I3, the cold condensed refrigerant will beheated by heat from the hot refrigerant vapor in the conduit 46 passingthrough both of the heat exchange units I8 and I 8 to thereby controlthe temperature of the cold refrigerant and to maintain it above apredetermined minimum to prevent damage to the compressor 28 andfrosting of the heat exchange means 28. If less heat is required, thevalves I4 and I5 may be closed and the valve I3 opened to cut the unitI8 out of the circuit and retain the heat of the unit I8 in the circuit,thu illustrating the selectivity and flexibility of the system in thisregard. It will be understood that instead of the heat exchange units I8and I8, means may be provided for supplying heat externally of thecircuit to the cold refrigerant before entering the compressor.

COOLING CYCLE For the cooling cycle, the valves 5, 1, 8, II will be openand the valves I, 2, 3, 4, 6, I3, I4 and I5 will be closed.

To maintain the material. as liquefied by the above-describedoperations, at a low temperature and corresponding pressure, starting atthe high pressure side of the compressor 28, and with the valves 2, 4, 6and I8 closed, and the valves 5 and 8 open, the refrigerant passes fromthe compressor through the conduit 66, the conduit 44, the valve 5, theconduit 42,.the heat exchange means 26 now acting as a condenser, theconduit 18, the conduit 52, the valve 8 and the conduit 36, into theliquid receiver wherein the cooled condensed refrigerant is collected.

The cooled refrigerant passes from the receiver 22 through the conduit31, through the dehydrator 23 and with the valve 3 closed, and the valve8 open, the liquid passes through the conduit 62 and the valve 8 to theexpansion valve 28, whereupon, with valve 1 open, and valves I and I2closed, the liquid passes through the nipple I82 to the coil means I1 inthe tank I6 where the expanded refrigerant removes heat from the liquidmaterial. With the valve II open, and the valve 6 closed, the expandedrefrigerant leaving the coil means I1, passes through the nipple I16,the conduit 46, and valve II, the conduit 58 and the conduit 64 to thesuction side of the compressor 28, to complete the refrigerating cycle.

After the above-described cooling cycle has been set up as stated, theliquid material is automatically maintained at a predeterminedtemperature by means, such as a switch, controlled by a pressureresponsive device connected to the tank I6 near its discharge end, foropening and closing the motor circuits of the fan 21 and the compressor28.

8 and I8, I2,

The system shown in Figure 3 Referring to Figure 3, in whichcorresponding parts are designated by corresponding reference charactersthe system is substantially the same as in Figure 1, except that therefrigerant always flows in the same direction through the coil I1. Thisresult is obtained with only slight changes from the arrangement ofFigure 1., such as the omission of the conduit 48, and the rearrangementof the conduit 58, the valve II, the conduit 62, the valve 8, theexpansion valve 28 and the valve 1, as will fully appear in thefollowing description of the heating and cooling cycles.

For the heating cycle, valves I, 2, 3, 4, 6 and I8 will be open, and thevalves 5, 1, 8, 8,, II, I2, I3, I4 and I5 will be closed.

In operation, starting at the high pressure side of the compressor 28,compressed hot refrigerant vapor passes from the compressor, through thevalve 6 and the conduit 48 to the upper end of the coil I1. From thebottom end of the coil I1, the condensed cooled refrigerant travelsthrough the valve I and the valve 2 to the liquid receiver 22. From thelatter, the liq- For the cooling cycle, the valves I, 5, 1, 8, 9

and II will, be open, and the valves 2, 3, 4, 6, III,

I2, I3, I4 and I5 will be closed.

Starting at the high pressure side of the compressor 28, the refrigerantpasses from the compressor, through the valve 5, the heat exchange means26, the conduit 52, and the valve 9 into the liquid receiver 22. Thecooled refrigerant passes from the receiver 22, through the dehydrator23, the conduit 62, the valve 8, the expansion valve 20 and the valve Ito the upper end of the coil l1. From the lower end of the coil II, theheated refrigerant passes through the valve I, the valve II and theconduit 50 to the suction side of the compressor 28, to complete therefrigeration cycle.

After the above-described cooling cycle has been set up, the liquidmaterial is automatically maintained at a predetermined temperature, as

'by the switch and pressure responsive device mentioned in connectionwith Figure 1.

The system shown in Figure 4 Referring to Figure 4, in whichcorresponding parts are designated by corresponding referencecharacters, the system is similar to those of Figure 1 and Figure 3,with one exception residing in the substitution of thermostaticexpansion valves N6 and E98 for the automatic-or fixed orifice expansionvalves 20 and 24, respectively, and a consequent exception in theomission of the heat exchange units 98 and t9, the valves i2, I3, I4 andI5, and accompanying conduits.

A thermostatic bulb 200, associated with the conduit 34, is connected bya conduit 202, to the expansion valve I96, and a thermostatic bulb 204,associated with the conduit 52, is connected, by a conduit 285, to theexpansion valve I98.

For the heating cycle, the valves 2, 3, 4, 6 and III will be open, andthe valves 5, I, 8, 9 and II will be closed.

Starting at the high pressure side of the compressor 28, the hotrefrigerant passes through the valve 6, and the conduit 46 to the upperend of the coil IT. From the bottom of the coil, the cool refrigeranttravels through the valve 2 to the liquid receiver 22, and from thelatter through the dehydrator 23 and the valve 3 to the expansion valveI98. Expanded in the latter, the refrigerant flow continues through thevalve 4, the heat exchange means 26 and the valve III to the suctionside of the compressor 28, to thus complete the heating cycle.

For the cooling cycle, the valves 5, I, 8, and 9 and II' will be open,and the valves 2, 3, 4, 6 and I8 will be closed.

Starting at the high side of the compressor, the refrigerant passesthrough the valve 5, the conduit 42, the heat exchange means 26, theconduit 52, and the valve 9 to the liquid receiver 22. From the latter,the refrigerant passes throughthe dehydrator 23, the valve 8, theconduit 62, the expansion valve I96 and the valve I to the upper end ofthe coil II. From the lower end of the coil II, the refrigerant flowsthrough the conduit 34. the valve II and the conduit 50 to the suctionside of the compressor 29, to complete the cooling cycle, which maythereafter be automatically effected as above pointed out.

It will be seen, from the foregoing description, that the presentinvention provides an improved method and apparatus, whereby a largequantity of a normally gaseous phase changeable material may be stored,in the liquid state, in a single container or tank, the material beingintroduced to the tank as a solid. The latter feature has manyadvantages of handling the material both before and during the operationo'f charging the container. A simplified reversible cycle refrigeratingsystem is advantageously utilized, both for liquefying the solidmaterial, or changing the temperature of liquid material at the time ofcharging, and thereafter maintaining the liquid at a predetermined tem--perature and vapor pressure best adapted for such storage. Furtheradvantages are thereby obtained, such as a reduction in weight, numberof parts and cost of the assembly as a 'whole. The apparatus is easy tomanufacture, assemble and operate, is a-compact self-contained unit, andis durable and reliable in service.

As various changes may be made in the form, construction and arrangementof the parts herein, without departing from the spirit and scope of theinvention and without sacrificing any of it advantages, it-is to beunderstood that all -matter herein is to be interpreted as illustrativeand not in any limiting sense.

It is also to be understood that the following claims are intended tocover all the generic and specific features of the invention hereindescribed, and all statements of the scope of the invention which, as amatter of language might be said to fall therebetween.

I claim:

1. In a system for liquefying solid normally gaseous phase changeablematerial and storing and maintaining the material in liquid phase at apredetermined temperature, the combination of chamber means adapted toreceive a charge of solid blocks of said material and store the materialin liquid phase, reversible cycle refrigerating means including heatexchange means in said chamber means for effecting heat exchange betweenhot refrigerant and solid material to effect liquefaction of the solidmaterial and cooling of the refrigerant and for effecting heat exchangebetween cold refrigerant and liquefied material to effect cooling of theliquefied material to maintain it at a predetermined temperature, andmeans for transferring heat from the hot refrigerant entering saidchamber means to the cooled refrigerant leaving said chamber means whilethe'cycle is operating in a direction to effect liquefaction of thesolid material.

2. In a system for liquefying solid normally gaseous phase changeablematerial and storing and maintaining the liquid material at apredetermined temperature, the combination of chamber means adapted toreceive a charge of solid blocks of said material and store liquidmaterial, reversible cycle refrigerating means including heat exchangemeans in said chamber means for effecting heat exchange between hotrefrigerant and said solid material to effect liquefaction of the solidmaterial and cooling of the refrigerant and for effecting heat exchangebetween cold refrigerant and liquid material to effect cooling of theliquid material, means for supplying heat to the cooled refrigerantwhile the cycle is operating in a direction 9 to effect liquefaction ofthe solid material, and mean for controlling the amount of heat suppliedby said last mentioned means.

3. In a system -for liquefying solid phase changeable normally gaseousmaterial and storil'ig and-maintaining the liquefied material at apredetermined temperature, the combination of means providing a chamberfor storing said material; and reversible cycle refrigerating meansincluding heat exchange means in vertical position in said chamber andmeans whereby refrigerant fiows through said heat exchange means from anupper to a lower portion thereof during each of said cycles.

5. In a system for liquefying solid normally gaseous phase changeablematerial and storing the liquefied material, the combination of anupright tank adapted to receive the solid material and to store theliquefied material therein, reversible cycle refrigerating meanincluding a cylindrical heat exchange coil in said tank adjacent theinner side wall thereof, said coil having a greater number ofconvolutions at the bottom than at the top of said tank, and acylindrical shield within the lower portion of said coil for protectingthe same against damage by impact from solid material when charging saidtank therewith. f

6. The method of handling normally gaseous phase changeable materials,which comprises establishing a supply of said material in solid phase,condensing a fluid heat exchange medium while in thermal contact withsaid supply to liquefy the material, and thereafter evaporating saidheat exchange medium while in thermal contact'with said supply towithdraw heat leaking into the supply of material from its surroundingsand thereby maintain the liquefied material at a predeterminedtemperature.

7. A method of handling normally gaseous phase changeable materialscomprising establishing a storage supply of solidified material in aconfined zone, circulating a refrigerant in heat exchange relation withthe supply of material while said refrigerant is vaporizedandconditioned to add heat to the material to thereby cause the materialto be liquefied and the refrigerant to be condensed. and thereaftercirculating the condensed refrigerant in heat exchange relation with thesupply of liquefied material in the confined zone while said condensedrefrigerant is conditioned to be evaporated and withdraw the heat leakininto the stored liquefied material from its surroundings and therebymaintain the liquefied material in the confined zone at a substantiallyconstant temperature and pressure.

8. A method of handling carbon dioxide comprising establishing a storagesupply of solid carbon dioxide in a confined zone, circulating arefrigerant in heat exchange relation with the solid carbon dioxidewhile said refrigerant is vaporized and conditioned to add heat to thecarbon dioxide to thereby cause the material to be liquefied and therefrigerant to be condensed, and thereafter circulating the condensedrefrigerant in heat exchange relation with the supply of liquefiedcarbon dioxide in the confined zone while said condensed refrigerant isconditioned to be evaporated and thereby withdraw the heat leaking intothe liquefied carbon dioxide from its surroundings and thereby maintainthe liquefied carbon dioxide in the confined zone at a sub-' stantiallyconstant temperature and pressure.

9. The method of llquefying solid normally gaseous phase changeablematerial and storing and maintaining the liquefied material at apredetermined temperature, which comprises confining a charge of solidmaterial in an enclosure, effecting heat exchange between hotrefrigerant and the confined solid material to effect cooling of therefrigerant and liquefaction of the material to produce a confinedcharge of liquefied material in the enclosure, and thereafter effectingheat exchange between cold refrigerant and the liquefied material whileconfined in the enclosure to maintain a confined charge of liquefied.material in the enclosure at a substantially constant temperature andpressure.

SIDNEY CLARKE MARSH.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Great Britain NOV. 21, 1934

9. THE METHOD OF LIQUEFYING SOLID NORMALLY GASEOUS PHASE CHANGEABLEMATERIAL AT A PREAND MAINTAINING THE LIQUEFIED MATERIAL AT APREDETERMINED TEMPERATURE, WHICH COMPRISES CONFINING A CHARGE OF SOLIDMATERIAL IN AN ENCLOSURE, EFFECTING HEAT EXCHANGE BETWEEN HOTREFRIGERANT AND THE CONFINED SOLID MATERIAL TO EFFECT COOLING OF THEREFRIGERANT AND LIQUEFRACTION OF THE MATERIAL TO PRODUCE A CONFINEDCHARGE OF LIQUEFIED MATERIAL IN THE ENCLOSURE, AND THEREAFTER EFFECTINGHEAT EXCHANGE BETWEEN COLD REFRIGERANT AND THE LIQUEFIED MATERIAL WHILECONFINED IN THE ENCLOSURE TO MAINTAIN A CONFINED CHARGE OF LUQUEFIEDMATERIAL IN THE ENCLOSURE AT A SUBSTANTIALLY CONSTANT TEMPERATURE ANDPRESSURE.